THE INTEL MICROPROCESSOR========================This article contains a few, very mildly edited pages from the Exam Cram Server+book byDeborah Haralson and Jeff Haralson (ISBN 1-58880-106-3). This document was typedupby Jonathan Smith.If you are interested in learning more, I suggest you buy the bookAnd now, on with the article...BOOK: Exam Cram Server+AUTHORS: Deborah HaralsonJeff HaralsonISBN:1-58880-106-3PAGES:71 - 78DATE:4:30 PM 8/20/2002Intel 8080----------The 8080 was first commercfially produced in 1974. It was the processor in theAltair 8800home computers. The Altair name comes from a Star Trek planet, which let thecomputer whereit has never gone before. This computer was placed on the market by the MITScalculatorcompany and was sold in kit form. Bill Gates and Paul Allen wrote the BASICprogramminglanguage for MITS, which was used on the Altair computer, and it started Bill'smeteoricrise to his present level of success.Intel 8086 and 8088-------------------The Intel 8086 was released on June 6, 1978. It was Intel's first 16-bitmicroprocessor.It was designed to be fast and powerful. The 8086 boasted a 4.77 to 10 MHzclock speed, 16-bit registers, and an external 16-bit data bus. It also had a 20-bit addressbus to address1MB of RAM. When IBM entered the computer business, the 8086 was considered tooexpensive,and oddly enough, too powerful to fulfill "Big Blue's" vision of a computer.The result wasthat Intel essentially "dumbed down" the 8086 processor and called it the 8088.At this point, some of the factors that affected the overall speed of a computercan reallybe identified. The 8086 and the 8088 could run the exact same program and couldbe set tothe exact same clock speed. The 16-bit data bus would let the 8086 import andexport thedata to the chip at twice the speed of the 8088.

Intel 80286-----------The Intel 80286, commonly called the 286, started as a 6 MHz speed demon. SoonIntel pushedthe envelope by upping the clock speed to 10, 12.5, and eventually 20 MHz. Toadd to thepower, the 286 came with a 24-bit address path that allowed for a whopping 16MBofaddressable memory. This chip was the heart of the IBM AT computer.The 286 also offered two modes of operations: real mode and protected mode.These twomodes of operation made the package operate like two separate chips in onepackage. Realmode operations essentially acted like an 8086 microprocessor. The computercould run the8088 and 8086 programs without requiring any modifcation to the programs. Everysysteminstruction was available and fully functional when the 286 was operating inreal mode.This level of compatibility came at a price. The 80286 microprocessoressentiallylobotomized itself, cutting back the addressable memory to 1MB. This made theold programs,not to mention the owner of the aformentioned programs, happy, but limited thefullflexibility and functionality of the machine.Protected mode operations allowed specially programmed applications manyadvantages over theolder real mode programs. Protected mode applications were "protected" in thatthey werelimited to writing only to their assigned memory. This helped to preventapplications fromstealing or overwriting areas of memory that was originally designated to aseparateapplication. The protected mode helped add stability and reliability to amachine that wasraplidly becoming indispensable in the business environment.The protected mode of operations also heralded in the invention of virtualmemory, whichallowed applications access to far more than the 16MB of physical memory. Thismeant thatwith up to 1GB of memory, larger applications coul be loaded simultaneously andwould beprotected from fighting each other for memory.Bill Gates' MS-DOS had a very tough time addressing this huge amount ofavailable storage, sothe 286 saw the rise of additional operating systems like Microsoft Windows, SCOUnix, andIBM's OS/2. The more powerful, true multitasking operating systems were stillin thedevelopment stage, and the 286 was obsolete by the time some of the "beefier"operating systemslike Windows 95, Windows NT, and Windows 2000 were introduced.One major disadvantage to the two modes in the 80286 microprocessor was that thecomputer

needed to be rebooted to change the operational mode. This led to a gradualshift from realmode applications to those natively written to take advantage of the manyfeatures of the 286.Intel 80386-----------Intel changed the world of computing when it introduced the 80386 microprocessorin June 16,1985. The 80386 was the first true 32-bit processor. All of the supportcircutry, theexternal bus, the address bus, and the registers were a full 32 bits in width.The chiporiginally shipped with a clock speed of 12 or 16 MHz and could address 4GB ofphysical RAMand 65TB of virtual memory. One of the biggest advantages of the 386 was that itcouldswitch between real and protected modes of operation without requiring a reboot.The 386 microprocessor introduced an additional operation mode known as virtualreal mode.This made it possible for the 386 processor to host virtual machines thatenabled more thanone application to actually run at the same time.Intel eventually produced 80386 processors that could run at 25 and 33 MHz.Clonemanufacturers weren't far behind as chief Intel rival, AMD, produced an 80386-compatiblethat ran at an unprecedented 40 MHz.Intel charged a pretty menny for the flagship of their processor fleet. The big80386 wasout of reach for many businesses, so Intel decided to offer a smaller versionthat wasdesigned to increase sales without dropping the price of the newest kid on theblock. InJune of 1988, Intel released the 386SX.386DX and 386SX---------------The 386DX (Dual word eXternal) was the full-blown 80386 in its entire 32-bitglory. The386SX (Single word eXternal) was created by disabling half of the 32 bits of thedata busto a single word or two bytes. This drop it to the 16-bit, 286 levels. Intelalso droppedthe memory addressing to a miserly 24-bits, which limited the SX machines toonly 16MB ofRAM.The one advantage of the 386SX was that it could be used to upgrade existing 16-bitmotherboards. This extended the life of users' machines and also temporarilyensured that